Present day commercial lightwave transmission networks use optical fibers to carry large amounts of multiplexed information over long distances from a transmit terminal to a receive terminal. Most long-haul transmission lines and a substantial portion of short-haul transmission lines such as inter-office and intra-office links, local area networks (LANs), metropolitan ea networks (MANs), and wide area network (WANs) are optical and, therefore, the information is carried over an optical fiber. A major advantage of transmitting information in optical form is the very large bandwidth and low losses associated with single mode optical fibers.
In practice, at the transmitting end of an optical fiber, electrical signals representative of intelligence are transformed into optical signals for transmission along the optical fiber and, at the receiving end, are transformed back into electrical signals for further processing. Furthermore, in today's networks, the optical signals are converted to electrical signals, and back to optical, in order to use electronic switches to switch the various channels to their destinations, and/or to perform electronic regeneration in very long links. This optical-to-electronic conversion within the network restricts the users to pre-specified signaling formats. It also makes the continuous upgrading and enhancement of the networks costly and cumbersome.
It is realized that with an all-optical network where optical signals can flow between users across the network without being converted to electronic signals within the network, the tens of terahertz of bandwidth available in optical fibers can be accessed in a more flexible and economic way. The benefits and advantages of being able to optically access the very broad bandwidth of optical fibers will permit a high-capacity, high speed network to be established for carrying data or information such as blueprints, words, music, medical and scientific images, movies, E-mail and the like from one location to another.
Some fundamental requirements that an all-optical transmission network should satisfy to realize the attainable benefits are as follows: First, the network must be universal in that it will accommodate an enormous diversity of applications, services, interfaces, protocols and signal formats. Second, it must be scalable in terms of the number of users, the data rate supported and the geographic span of the network. Third, to limit the cost and complexity of network nodes, the optical network must be "transparent" to high rate users so that the flow of their optical signals within the core of the network is unimpeded by optical-to-electronic transformations, even though that flow may be controlled by electronics.
A national or global network of an all-optical transmission system which meets the above noted requirements is currently needed.